1. Field of the Invention
The present invention relates to a package for electronic components and also relates to electronic components including such a package. The present invention particularly relates to a ceramic package for surface-mount type electronic components and electronic components using such a ceramic package.
2. Description of the Related Art
A conventional package for an electronic component includes wiring layers disposed in recesses provided on the side surfaces of a substrate (castellation), as well as, via-holes arranged along the direction of thickness of the substrate in order to electrically connect electrodes located on an upper surface of a base substrate and electrodes disposed on the bottom surface of the base substrate.
FIGS. 19 to 21 show common structures of a conventional ceramic package provided with recesses on the side surfaces of a substrate. FIGS. 19 and 20 show a disassembled perspective top view and a perspective bottom view of the conventional package, respectively, while FIG. 21 shows a partially enlarged perspective view of the package in FIG. 20. The package 21 is composed of a base substrate 22 and a side wall 23. The base substrate 22 and the side wall 23 include layer or a plurality of layers of a ceramic insulation substrate made of, for example, Al2O3. An electrode 24 (the area surrounded by a broken line in FIG. 19) for electrically connecting device elements (not shown) to the package 21 is provided on the element mounting surface for mounting device elements, or on the upper surface of the base substrate 22. External electrode terminals 25 for electrically connecting the package 21 to a mounting substrate are formed on the bottom surface of the base substrate 22. Recesses 26 and 30 communicating with the bottom surface of the base substrate 22 are provided at the side surfaces of the side wall 23 and base substrate 22, and wiring layers 27 are disposed on the side surfaces of the recesses 26 provided on the base substrate 22. The recesses 26 and 30 have the same cross-sectional shape as each other. The electrode 24 is electrically connected to the external electrode terminals 25 through lead patterns 28 (the area outside of the area surrounded by the broken line in FIG. 19), which abut the electrode and extend outward, and the wiring layers 27 are disposed in the recesses 26. Chamfers 31 and 31 are provided at the corners of the base substrate 22 and side wall 23 in order to prevent them from being chipped.
The method for manufacturing the package as described above will be described hereinafter. Through holes which define the recesses 26 and the chamfers 31 are formed on a mother sheet of a ceramic green sheet provided for forming the base substrate 22, followed by depositing a metal film for forming the wiring layers 27 in the recesses 26 and on the electrodes 24, 28 and 25. Subsequently, the area surrounded by the side wall 23 is punched, and through holes defining the recesses 30 and chamfers 31 are formed through a mother sheet of a ceramic green sheet for forming the side wall 23. These ceramic green sheets for forming the base substrates and side walls are laminated, press-bonded and fired in the next step. Then, the surfaces of the electrodes 24 and 25, and the surfaces of the wiring layers 27 are plated. Finally, the laminated green sheet is cut along the lines passing through the centers of the through holes that define the recesses and chamfers to divide into a lot of substrates, thereby completing the package 21.
FIG. 22 is a cross-sectional view showing the configuration when an electronic component 35 including the package 21 in which an electronic device element is accommodated is mounted on a substrate. The package 21 in FIG. 22 corresponds to a cross-section of the package in FIG. 20 on the surface Y. An electronic device element 32 such as an elastic surface wave element or a semiconductor element is mounted on the element mounting surface of the package 21 as shown in the drawing, and the package 21 is airtight-sealed with a lid 29 made of, for example, a metal. The electronic component formed as described above is mounted on the surface of a printed circuit board 34 using a solder for mounting. In mounting the electronic component, solder fillets 33 are formed by a reflow method using a solder paste. The solder fillets 33 are provided for electrically and mechanically connecting the electronic component 35 to the printed circuit board.
However, the conventional package 21 for an electronic component experienced the problems as described below. While the thickness W of the side wall 23 of the package is reduced as the electronic component is miniaturized, the thickness W of the side wall 23 as a sealing width should be ensured to a certain extent for airtight-sealing of the package using the lid 29. Since the thickness W of the side wall 23 turns out to be a minimum (Wmin) particularly at the portions where the recesses 26 and 30 are formed, the recesses 26 and 30 are required to be as small as possible for providing a certain minimum required sealing width.
A thicker electrical continuity passage can be formed, on the other hand, between the external electrode terminal 25 and the electrode 24 on the element mounting surface as the contact area between the solder fillet 33 and the wiring layer 27 is wider, thereby impedance Z, for example resistance, between the electrodes is reduced. In addition, mechanical strength such as bonding strength and bending strength can be enhanced as the contact area between the solder fillet 33 and the wiring layer 27 is wider. Accordingly, the recesses 26 and 30 should be formed to be as large as possible, in order to increase the contact area between the solder fillet 33 and the wiring layer 27, or to ensure a good electrical and mechanical continuity between the element and the printed circuit board.
In order to overcome the problems described above, preferred embodiments of the present invention provide a package for electronic components having excellent electrical and mechanical continuity with a printed circuit board and being highly airtight, and electronic components using the same as a surface-mount type electronic component in which an electronic device element is accommodated in the package.
According to a preferred embodiment of the present invention, a package for electronic components includes a base substrate and a side wall in which recesses communicating with the bottom surface of the base substrate are provided on the base substrate and the side wall, and in which electrodes on the bottom surface of the base substrate are electrically connected to electrodes on the element mounting surface defining an upper surface of the base substrate though wiring layers disposed on a portion of the recesses, wherein the recesses are arranged on the base substrate to have a cross-sectional area that is wider than the cross-sectional area of the recesses disposed on the side wall.
When the recesses on the base substrate have a wider cross-sectional area than the cross-sectional area of the recesses on the side wall standing on the base substrate among the recesses on the base substrate and on the side wall, or when the recesses on the side wall are smaller and the recesses on the base substrate are larger, the thickness of the side wall of the package defining a sealing width can be ensured to a certain extent even at its narrowest portion, besides maintaining a sufficient a contact area between the wiring layer and solder fillets so as to ensure electrical continuity between the electrodes on the bottom surface of the base electrode and the electrodes on the element mounting surface. Consequently, excellent electrical and mechanical continuity between the electronic component and the printed circuit board are achieved while maintaining the package airtight.
The recesses may be also provided at the corners of the package. The wiring layer may be provided on the side surfaces of the recesses on the base substrate, and also at the upper portions of the recesses, or at the bottom portions of the material constituting the side wall. When the area of the wiring layer is enlarged as described above, a wider contact area between the wiring layer and the solder fillet can be ensured to further improve the electrical and mechanical continuity between the package and base substrate.
According to this unique structure and arrangement, the recesses on the base substrate preferably have a larger cross-sectional area than the cross-sectional area of the recesses on the side wall standing on the base substrate. Accordingly, the thickness of the side wall as a sealing width of the cap can be ensured to a certain extent even at the narrowest portion, while sufficiently ensuring the contact area between the wiring layer and the solder fillet for electrically connecting the electrodes on the bottom surface of the base substrate to the electrodes on the element mounting surface. Consequently, excellent electrical and mechanical continuity between the electronic component and the printed circuit board is ensured while keeping the package airtight to prevent the electrical characteristics of the electronic device element from being deteriorated.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.